Pressure regulation stations are used to control the pressure in gas distribution systems. Most modern day gas distribution systems require multiple layers of protection to prevent the pipeline downstream of a regulation station from being over pressurized and potentially failing. National, international and local codes, statutes, laws and operational practices govern the requirements of a particular installation. Slam shut valves are used in natural gas systems to provide an additional layer of protection by shutting off the flow of gas. In many areas of the world, slam shuts are required by statute or law.
Each layer of protection adds to the cost of installation and operation of a distribution system. While the cost of purchasing and installing added equipment is intuitive, the larger operational cost is more complex. Each layer of pressure protection must be allocated a pressure range in which it operates. This range is between the maximum pressure the pipeline is rated for and its normal operation pressure. The width of the pressure range is a function of the equipment's accuracy. The impact of a lower pipeline operating pressure is a lower flow rate of gas in the distribution system.
Slam shut valves can be designed for use with a pressure reducing regulator to provide secondary downstream pressure protection. Such valves can be designed to shut off the flow of gas when the sense or outlet pressure in the system either exceeds or drops below set point pressures. Historically, slam shut valves typically include: a pressure sensing element that directly operates a latch holding the slam shut valve open; and a spring actuated closing element which may be a plug or flapper that closes against a seat. A typical prior art slam shut valve is included as FIG. 1. Accuracy and repeatable performance are significantly affected by differing designs and types of latching mechanisms. Disadvantages of the prior art include the valve closing at too low or high of a pressure due to vibration, valve leaks, variations in trip pressure due to wear and contamination requiring a maintenance crew to be dispatched. The cost of ownership is increased by the inventory of multiple springs and diaphragms are necessary to vary the set pressures.